October 24, 2012

Scientists Complete Giant Mirror For Giant Magellan Telescope

Scientists have completed the most challenging large astronomical mirror ever created.

The mirror will be part of the 82-feet Giant Magellan Telescope, which will be exploring planets, and the formation of stars, galaxies and black holes in the early universe.

The team has been working for the past several years on a 27.5-feet diameter mirror with an unusual, highly asymmetric shape.

The "degree of difficulty" for the mirror is 10 times that of any previous large telescope mirrors, according to the University of Arizona.

The mirror surface matches the desired prescription to a precision of 19 nanometers, and is so smooth that if it were the size of the continental U.S., the higher mountains would be a little more than a half-inch high.

The mirror will form the heart of the Giant Magellan Telescope, providing more than 4,000 square feet of light-collecting area.

"Making this first GMT mirror required all the expertise and experience that the University has built up over 25 years of making telescope mirrors and a great deal of innovation to push beyond previous limits in optical fabrication and testing," said Buell Jannuzi, director of the UA Steward Observatory and professor of astronomy. "In achieving this remarkable milestone, the team built and demonstrated all the equipment and techniques that will lead to efficient production of the remaining mirrors for the GMT.”

The mirror was cast at the mirror lab from 20 tons of glass, melted in a rotating furnace until it flowed into a honeycomb mold.

Scientists at the lab used a series of fine abrasives to polish it once the glass had cooled and the mold material was removed.

“We need to be certain the off-axis shape of this mirror, as well as the other six that will be made for GMT, is precisely right, to an accuracy of 1/20 of a wavelength of light,” said Buddy Martin, polishing scientist at the Mirror Lab. “Only then will the seven large mirrors form a single, exquisitely sharp image when they all come together in the telescope in Chile. We have now demonstrated that we can fabricate the mirrors to the required accuracy for the telescope to work as designed.”

The telescope will be located on a remote mountaintop in the Chilean Andes, where the skies are clear and dark.

“The technical achievements at the UA´s mirror lab and the dedication and commitment of our national and international partners will allow us to open a new window on the universe. An exciting future of discovery awaits us," added Wendy Freedman, chair of the GMT board.

The Giant Magellan Telescope will begin operations late in the decade, and will allow astronomers and students to address questions in cosmology, astrophysics and planetary science.

"The Giant Magellan Telescope has the potential to transform how we see the cosmos, and our place in it," concluded Matthew Colless, director of the Australian Astronomical Observatory.